Before you ask, no. I had nothing to do with this.
Basically, to quote TechCrunch
To access the hidden feature, open Google Earth and hit Command+Option+A (note it must be capital A) or Ctrl+Alt+A if you're using a Windows Machine.
However, given my obvious conflict of interest, I'll just take exception to TechCrunch's final statement:
…It wasn't perfect, but it was as good visually as the paid Microsoft Flight Simulator, and in terms of actually presenting real objects it was better…
Obviously they haven't looked at FSX. The two products have both different visual focusses and merits. How does the terrain and imagery look outside of major cities? How do those airports compare? How are the flight systems? ATC?
I'll just stop now before I dig myself into a hole :-)